Fixed a bug in the Transaction class that would skip on the AsyncEnded subscriber callbacks if a subscriber unsubscribed during the callback (either in the callback thread or asynchronously at the same time); wrote a unit test that highlights the bug

git-svn-id: file:///srv/devel/repo-conversion/nusu@125 d2e56fa2-650e-0410-a79f-9358c0239efd

Source/Tracking/Transaction.Test.cs

@@ -62,6 +62,46 @@ namespace Nuclex.Support.Tracking {
 
     #endregion // class TestWiatable
 
+    #region class UnsubscribingTransaction
+
+    /// <summary>Transaction that unsubscribes during an event callback</summary>
+    private class UnsubscribingTransaction : Transaction {
+
+      /// <summary>Initializes a new unsubscribing transaction</summary>
+      /// <param name="transactionToMonitor">
+      ///   Transaction whose AsyncEnded event will be monitored to trigger
+      ///   the this transaction unsubscribing from the event.
+      /// </param>
+      public UnsubscribingTransaction(Transaction transactionToMonitor) {
+        this.transactionToMonitor = transactionToMonitor;
+        this.monitoredTransactionEndedDelegate = new EventHandler(
+          monitoredTransactionEnded
+        );
+
+        this.transactionToMonitor.AsyncEnded += this.monitoredTransactionEndedDelegate;
+      }
+
+      /// <summary>Called when the monitored transaction has ended</summary>
+      /// <param name="sender">Monitored transaction that has ended</param>
+      /// <param name="arguments">Not used</param>
+      private void monitoredTransactionEnded(object sender, EventArgs arguments) {
+        this.transactionToMonitor.AsyncEnded -= this.monitoredTransactionEndedDelegate;
+      }
+
+      /// <summary>Transitions the transaction into the ended state</summary>
+      public void End() {
+        OnAsyncEnded();
+      }
+
+      /// <summary>Transaction whose ending in being monitored</summary>
+      private Transaction transactionToMonitor;
+      /// <summary>Delegate to the monitoredTransactionEnded() method</summary>
+      private EventHandler monitoredTransactionEndedDelegate;
+
+    }
+
+    #endregion // class TestWiatable
+
     /// <summary>Initialization routine executed before each test is run</summary>
     [SetUp]
     public void Setup() {
@@ -167,6 +207,23 @@ namespace Nuclex.Support.Tracking {
       Assert.IsTrue(test.Wait(TimeSpan.Zero));
     }
 
+    [Test]
+    public void TestUnsubscribeInEndedCallback() {
+      TestTransaction monitored = new TestTransaction();
+      UnsubscribingTransaction test = new UnsubscribingTransaction(monitored);
+
+      ITransactionSubscriber mockedSubscriber = mockSubscriber(monitored);
+      
+      try {
+        Expect.Once.On(mockedSubscriber).Method("Ended").WithAnyArguments();
+        monitored.End();
+        this.mockery.VerifyAllExpectationsHaveBeenMet();
+      }
+      finally {
+        test.End();
+      }
+    }
+
     /// <summary>Mocks a subscriber for the events of a transaction</summary>
     /// <param name="transaction">Transaction to mock an event subscriber for</param>
     /// <returns>The mocked event subscriber</returns>

Source/Tracking/Transaction.cs

@@ -103,21 +103,25 @@ namespace Nuclex.Support.Tracking {
       }
       remove {
 
+        if(!this.ended) {
           lock(this) {
+            if(!this.ended) {
 
               // Only try to remove the event handler if the subscriber list was created,
               // otherwise, we can be sure that no actual subscribers exist.
               if(!ReferenceEquals(this.endedEventSubscribers, null)) {
                 int eventHandlerIndex = this.endedEventSubscribers.IndexOf(value);
 
-            // Unsubscribing a non-subscribed delegate from an event is allowed and should
+                // Unsubscribing a non-subscribed delegate from an event is allowed and
-            // not throw an exception.
+                // should not throw an exception.
                 if(eventHandlerIndex != -1) {
                   this.endedEventSubscribers.RemoveAt(eventHandlerIndex);
                 }
               }
 
             }
+          }
+        }
 
       }
     }
@@ -202,9 +206,9 @@ namespace Nuclex.Support.Tracking {
       lock(this) {
 
         // No double lock here, this is an exception that indicates an implementation
-        // error that will not be triggered under normal circumstances. We don't want
+        // error that will not be triggered under normal circumstances. We don't need
         // to waste any effort optimizing the speed at which an implementation fault
-        // will be noticed.
+        // will be reported ;-)
         if(this.ended)
           throw new InvalidOperationException("The transaction has already been ended");
 
@@ -214,21 +218,20 @@ namespace Nuclex.Support.Tracking {
         // the event after we just saw it being null, it would be created in an already
         // set state due to the ended flag (see above) being set to true beforehand!
         // But since we've got a lock ready, we can even avoid that 1 in a million
-        // performance loss and prevent a second doneEvent from being created.
+        // performance loss and prevent the doneEvent from being signalled needlessly.
         if(this.doneEvent != null)
           this.doneEvent.Set();
 
       }
 
-      if(!ReferenceEquals(this.endedEventSubscribers, null)) {
-
       // Fire the ended events to all event subscribers. We can freely use the list
       // without synchronization at this point on since once this.ended is set to true,
       // the subscribers list will not be accessed any longer
+      if(!ReferenceEquals(this.endedEventSubscribers, null)) {
         for(int index = 0; index < this.endedEventSubscribers.Count; ++index) {
           this.endedEventSubscribers[index](this, EventArgs.Empty);
         }
-
+        this.endedEventSubscribers = null;
       }
 
     }